There is a demand for sewing thread that is highly resistant to fire and heat for sewing together layers of fire-retardant fabrics such as for use in bedding, institutional window treatments, and for protective safety apparel. Impending U.S. Government regulations will mandate the use of such threads in products such as bedding, by as early as Jul. 1, 2007. Currently, the predominant product used for these type applications is made from para-aramid staple fibers such as Kevlar® or Twaron®. Because the elongation prior to breakage of these fibers is inherently low, such fibers typically exhibit less than exemplary sewing performance, such that sewing yarns produced from these fibers generally must be produced in very fine counts with at least two or three plies. The cost of such sewing yarns also can be exceptionally high due to their upwards of 100% content of very expensive para-aramid fibers.
For example, U.S. Pat. No. 7,111,445 to Kolmes and Threlkeld, discloses a fire resistant yarn and products made therefrom, with the composite yarn comprising a core of a conventional, non-fire-retardant strand. A fire-retardant, low-elongation yarn is wrapped around this core, followed by an outer wrap of a non-fire retardant yarn applied in the opposite direction. A bonding agent and a lubricant are applied in a final step. When exposed to high heat and/or flames, the core and outer sheath purportedly will melt and burn, leaving the inner wrapping intact with sufficient strength to hold together the layers of fabric. The chief advantage cited by this patent is that the low percentage of high-cost para-aramid yarns used yielding a substantially less expensive thread than conventional fire retardant yarns. However, there are disadvantages not disclosed that should be obvious to one skilled in the art. For example, the predominant fibers used in the core and outermost wrap that melt and/or burn at relatively low temperature can release toxic fumes into the environment. The residual para-aramid inner sheath remaining after such burn-off generally will have only a fraction of the tensile strength of conventional heat resistant yarns, and the bonding operation required often is very capital intensive and thus negates much of the claimed raw materials savings.
Therefore, it can be seen that a need exists for a more economical heat and fire-retardant sewing thread that addresses the foregoing and other related and unrelated problems in the art.